@ Ike,Lloyd Irving
Aztually Dialga,Palkia, and Giratina, in my opinion, is a trio of deities, so in a way they are superior to a dragon trio, since in all references i.e. show, movies, and game, they are refered to as deiies not just dragons. and how else would they be able to control Time, Space, and Antimatter respectively? answer: cause they are, in a way gods.

sinnoh deity chain: Arceus=Creator
Palkia=creator of the dimensions of space. lesser to arceus
Dialga=creator of temporal dimensions. lesser to arceus
Giratina= creator of antimatter. banished to the Distorted world. lesser to Arceus
uxie=shaper of human knoledge.lesser to arceus
Mespirit=shaper of human emotion. lesser to arceus
Azelf=shaper of human willpower. lesser to arceus

Also in unova there are three trios. there is the dragon hero trio: Zekrom, Reshiram, Kyrum
the trio of the winds: Tornadus,Thundurus, and Landorus
and the swordsmen: Cobalion, Terrakion, and Virizion